It has long been known in the building art that stonework, for example coping, reglets, balustrades or belt courses, must have sealed joints between adjacent stones, and between stones and adjacent masonry. Buildings move, and stonework, being used to finish or delimit the periphery of building structures, is usually at the point of maximum movement. Failure of the joint, with consequent degradation of the masonry and building structure from water intrusion, is a major construction problem.
Current practice in the art is to clean and fill the joint with a caulk or sealant, usually a structural sealants such as are manufactured by the General Electric Company, Dow Corning, Pecora and others. So long as the sealant bonds to the stone work, and is itself protected from environmental damage, the joint seal will remain good.
Addressing coping as an example, protection of the sealant may be accomplished by capping the sealant with a protective outer strip, such as Weathercap, a trade marked lead protective joint covering. This joint cover must be embedded in the basic joint sealant.
In order to properly bond the joint, and afford any protective cover, the joint sealant must be placed within the joint to a depth which is a function of the joint width. The joint itself may be of greater depth, and may have effectively infinite depth, as in parapets and reglets, due to a relatively large open area behind the joint. The joint integrity requires bonding of sealant to the stone and protective strip, by restraining injection of sealant with backer rod or bond breaker tape emplaced in the joint.
Backer rod is a continuous foam, expanded in shape, either of open or closed cell composition, which is compressed in place between stones to limit depth of sealant and to serve as a post dam. Use and selection of an appropriate backer rod or bond breaker tape is specified by the manufacture's instructions for the chosen breaker rod or bond breaker tape.
Proper standards for a joint seal are called forth in ASTM Standard Guide C 962-86, published September 1986, on the use of Elastomeric Joint Sealants.